Provisionally named "Successor" (being the successor to the Vanguard class SSBNs), it was officially announced in 2016 that the first of class would be named Dreadnought, and that the class would be the Dreadnought class.[6][7] The next three boats will be called Valiant,[8]Warspite and King George VI.[9]

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Since the retirement of the last Royal Air ForceWE.177 nuclear bomb in 1998, the British nuclear arsenal has been wholly submarine-based. It is intended to deter a potential enemy because they cannot ensure eliminating the entire stockpile in a first strike if a ballistic missile submarine remains undetected.

Since the Strategic Defence Review (SDR), the UK has maintained a stockpile of around 215 warheads, with around 120 active (usable). Under the continuous at sea deterrence policy, at least one Vanguard-class SSBN is kept on patrol with up to 16 Trident missiles sharing up to 48 warheads from the stockpile at any given time. The SDR considered this was the minimum number of warheads adequate for deterrence. It is collectively known as the Trident system.[10] The majority of this system is based in Scotland at HMNB Clyde (HMS Neptune), which includes the Faslane home of the Vanguard submarines, and at RNAD Coulport. The oldest Vanguard-class submarine is expected to remain in service until 2019[11] without a refit. Since 1998, the system has also provided the Government with the option of a lower-yield, "sub-strategic" nuclear strike capability.[12] Under both the Strategic Defence and Security Review 2010 and the Strategic Defence and Security Review 2015, the total number of warheads for the submarine on patrol will be 40 and the maximum total number of ballistic missiles will be 8.[13][14]

In May 2011 the government approved the initial assessment phase for the new submarines and authorised the purchase of long lead-time items including steel for the hulls. In May 2015 the Conservative Party won the UK General Election on a manifesto which included a commitment to maintaining a CASD with four Successor submarines.[15] The final decision to commit to the Successor programme was approved on 18 July 2016 when the House of Commons voted to renew Trident by 472 votes to 117.[16]
Successor has generated controversy because of its cost,[17] and because some political parties and campaign groups such as the Campaign for Nuclear Disarmament (CND) and Trident Ploughshares oppose the retention of CASD or any nuclear weapons by the UK on moral or financial grounds.[18][19]

Construction started in late 2016 at the Barrow-in-Furness shipyard operated by BAE Systems Maritime – Submarines, when the first submarine was provisionally expected to enter service in 2028.[20] The start of construction of the second phase was announced in May 2018.[21]
As of 2018[update], the Ministry of Defence (MoD) expects the submarines to enter service in the early 2030s, for a cost of £31 billion. The submarines will have an intended service life of around 35 to 40 years, an increase of around 25% over the previous class.[22] The MoD said in December 2018 that construction of the first submarine was on schedule and within budget.[23]